1. Technical Field
The present disclosure relates to razor blades in general, and to razor blades with surface coatings in particular.
2. Background Information
Razor blades are typically made of a suitable substrate material such as stainless steel, and a cutting edge is formed with a wedge-shaped configuration with an ultimate tip having a radius less than about 100 nm, such as about 20 to 30 nm. Hard coatings such as diamond, amorphous diamond, diamond-like carbon (DLC) material, nitrides, carbides, oxides or ceramics are often used to improve strength, corrosion resistance and shaving ability, maintaining needed strength while permitting thinner edges with lower cutting forces to be used.
It is known from the art, for instance from U.S. Pat. Nos. 3,743,551 and 3,838,512, that the shaving properties of a razor blade can be improved by applying a polymer outer surface coating (e.g., polytetrafluoroethylene—“PTFE”). Typically, polymer coatings of this type are applied to create a relatively thin layer (e.g., equal to or less than 500 nm) on at least the tip of the blade. The layer can be applied using a variety of different techniques; e.g., spray application, bath dipping, etc. Since no application process will apply a perfectly uniform layer thickness across the entire desired surface, the thickness of the initially applied layer is typically chosen to ensure adequate layer thickness given an expected thickness variation. Although this “relatively” thin layer ensures adequate layer thickness, it is not optimum for shaving; e.g., it is too thick. During the first few strokes of use of a new coated blade, a portion of the polymer coating (if left at the initial thickness) will be removed from the tip during the shaving process by the user of the blade. This process of moving the surface coating by the user of the blade via contact is sometimes referred to as “push back” or “peel back” of the coating. After the excess polymer coating is “pushed back” by the user, a much thinner layer of polymer coating (a layer that can be one polymer molecule thick) typically remains on the blade edge throughout the useful life of the blade. Until the initial thickness of the polymer coating is “pushed back,” however, the user can experience some amount of discomfort.
U.S. Pat. Nos. 5,985,459 and 7,247,249 disclose treating a razor blade cutting edge having an adherent polyfluorocarbon coating with a solvent to partially remove some of the coating, apparently to potentially avoid the aforesaid discomfort associated with the excessively thick coating. Using a solvent can significantly add to the manufacturing cost, and in some instances add additional manufacturing steps. For example, the '459 Patent discloses that in some instances a post-solvent treatment step can be used to remove any excess solvent.